1. Field of Invention
The present invention relates to an auxiliary power distribution system operable to provide uninterruptible power to various critical loads and/or power outlets.
2. Background and Prior Art
Class-2 electrical circuits have long been used as the basis for auxiliary power distribution systems in private, public and commercial buildings, their main applications being limited to powering door chimes, thermostats, etc. However, these Class-2 circuits are normally powered from a regular electric utility power line, without any source of back-up power, and are therefore subject to occasional power interruptions. Thus, this type of Class-2 auxiliary power distribution system is not effective in providing power to loads that should not suffer power interruptions--loads such as computer terminals, emergency lighting, telephone terminals, PBX systems, smoke/fire alarms, intrusions alarms, etc.
According to Article 725 of NATIONAL ELECTRICAL CODE 1984--issued by NATIONAL FIRE PROTECTION ASSOCIATION, BATTERYMARCH PARK, Quincy, Mass. 02269--as long as output current may exceed 0.005 Amp, a Class-2 electrical circuit is limited to a maximum output voltage of 30 Volt RMS for sinusoidal voltages at power line frequencies. Based on experience, this voltage level is considered to be acceptably safe from electric shock hazards.
A wide variety of Class-2 transformers and power supplies are available for purchase. An example of a Class-2 transformer is a so-called bell-transformer, as typically used for powering a door chime or a thermostat. An example of a Class-2 power supply is a plug-in battery eliminator for a hand-held calculator.
At frequencies substantially higher than 60 Hz, the human body exhibits a significant degree of so-called skin-effect; which causes less penetration of current into the human body while at the same time making the human body more resistive to the flow of current.
For instance, at a frequency of 60 Hz, it is relatively harmless for a person to receive an electric shock that results in a current as high as 0.005 Amp. At 30 kHz, on the other hand, it is about equally harmless for a person to receive an electric shock that results in a current as high as 0.03 Ampere.